This invention relates generally to mass airflow sensors, and more specifically it relates to the elimination of turbulence for a silicon micromachined airflow sensor.
In state-of-the-art electronically controlled fuel systems for automotive internal combustion engines, the measurement of airflow that is inducted into the engine's intake system is an input to the engine electronic control unit (ECU). One way of obtaining this measurement is by means of a mass airflow sensor located in a by-pass venturi in an airbody. One type of mass airflow sensor comprises a silicon micromachined sensing element mounted on a ceramic substrate. The sensing element is disposed in the airflow through the by-pass venturi and provides a signal that is indicative of mass airflow into the engine.
It has been observed that certain irregularities in the airflow measurements by such sensors can occur, and it has been discovered that these are attributable to leading edge turbulence at the silicon micromachined sensing element. The present invention is directed to a solution to this problem.
A principal aspect of the solution involves the creation of a slot through the ceramic substrate at the leading edge of the silicon sensing element that is disposed on the substrate. It is also desirable for the leading edge of the silicon sensing element to have a sharp corner that points generally toward the direction of airflow so as to encourage a portion of the flow to pass through the slot while another portion of the flow passes smoothly over the sensing surface of the sensing element. The smooth flow over the sensing surface of the sensing element reduces spurious fluctuations in the measurements that would otherwise occur due to turbulence. Accordingly, a meaningful improvement is attained through the exercise of relatively uncomplicated fabrication procedures.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims, which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated for practicing the invention.